Natural Frequencies Of Torsional Vibration Research Articles

Study of the Influence of the Presence of Local Edge Damage on the Spectrum of Natural Frequencies of Torsional Vibrations of Cantilever Rods

Study of the Influence of the Presence of Local Edge Damage on the Spectrum of Natural Frequencies of Torsional Vibrations of Cantilever Rods

Identification of pathogenic bacteria using the spectra of native DNA molecules

The purpose of detecting low-frequency (relative to infrared and ultraviolet) resonance absorption of an electromagnetic field in the centimeter wavelength range using DNA molecules at a frequency corresponding to the natural frequency of torsional vibrations of the native DNA helix is to find a relationship between the length of DNA (its spectrum) and the type of a bacterium. Instead of DNA solution, cultures of different bacteria that contained DNA were used and the resonance frequencies of torsional vibrations of the helices in DNA molecules were calculated for them. The cultures were placed in test tubes or in a cuvette and were subjected to microwave irradiation. Theoretical analysis was carried out with respect to the DNA reaction to external centimeter radiation and the resonant DNA frequencies of three types of bacteria such as E. coli M17, M. avium and Mycobacterium tuberculosis were determined. Peak absorption of the ultrahigh-frequency electromagnetic field by bacterial cultures was detected at frequencies close to the calculated natural frequencies of torsional vibrations of DNA helices of the said types of bacteria: 10.271 GHz, 10.317 GHz and 10.356 GHz, respectively.

Bottomhole-Assembly Dynamics Software Helps Mitigate Twistoffs While Drilling

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202174, “Mitigating Twistoffs While Drilling With the Help of Bottomhole-Assembly Dynamics Software,” by Mario A. Rivas, SPE, Andres A. Ramirez, and Bader S. Al‑Zahrani, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. _ A major challenge during drilling operations is the occurrence of twistoffs on bottomhole assembly (BHA) components. To overcome this challenge, a study was performed of twistoffs experienced on BHA components. Based on the findings, drilling operations and recommendations were provided to reduce or eliminate twistoffs related to suboptimal drilling parameters. This analysis will help drilling engineers and personnel foresee vibration dysfunctions and act accordingly with the use of BHA dynamics software to optimize drilling parameters before and during drilling. Twistoffs Caused by Drillstring Vibrations Field experience has shown that unwanted drillstring vibrations lead to failures, especially stick/slip (torsional vibrations) that occurs approximately 50% of the time during drilling. Three main types of vibrations can be distinguished: torsional (stick/slip oscillations), axial (bit bouncing), and lateral (whirling motion caused by an imbalanced drillstring). These three types of vibration can occur at any time during drilling. Induced axial vibrations at the bit can lead to lateral vibrations in the drillstring and BHA, and axial and torsional vibrations can be observed at surface. Sometimes the severe axial vibrations close to the bit may not be observed at surface, which may lead to a potential twistoff if drilling parameters are not changed and optimized. Additionally, fatigue failure is intensified with high vibrational loads, specifically at curved well trajectories or in buckled drillstring sections as shown in Fig. 1, where high bending stresses occur. The most critical fatigue damage will happen when the drillstring is in resonance with one of its natural frequencies, resulting in twistoff events at a much lower drillstring component yield strength. The objective of the study described in the complete paper is to pursue an integrated approach considering the use of vibration-analysis software in the design of a BHA to identify safe operating windows for rotary speed and weight on bit (WOB) to prevent buckling and analyze fatigue. BHA Dynamics Resonance occurs when the rotary speed is very close to one of the natural frequencies for torsional vibration (the primary cause of failure), and WOB natural frequency for flexural vibrations of the BHA. When the frequency of any excitation is one of the natural drillstring frequencies, then the drillstring will resonate and vibration levels will be highest. With very high amplitudes, vibrations will accelerate drillstring and BHA fatigue. To estimate the critical rotary speed (resonance frequency), the BHA can be simulated using available BHA dynamics and vibration software. This software can analyze downhole vibrations; its simulations have matched several cases very closely to what the operator has experienced. Three different examples were analyzed and presented in the complete paper. The software uses nonlinear vibration theory to determine drillstring-resonance frequencies.

ОЦЕНКА РЕЗОНАНСНЫХ РЕЖИМОВ ПРИВОДА ГЛАВНОГО ДВИЖЕНИЯ ТОКАРНОГО СТАНКА С БЕССТУПЕНЧАТЫМ РЕГУЛИРОВАНИЕМ

The study objective is to define and evaluate the resonant drive modes of the lathe primary motion continuously rated. The problem to which the paper is devoted is to draw up a design scheme of a dynamic torsional drive system for the lathe primary motion with the spindle speed continuously rated and to make a calculation that allows finding out the lowest natural torsional vibration frequencies of the drive. Research methods: analysis of a multi-mass analytical model of the lathe drive primary motion, followed by its reduction to models with a smaller number of masses (inertial elements). The novelty of the work is in the development of software that allows simplifying linear dynamic systems and finding out natural frequencies. Study results: the dynamic quality of the drive is analyzed, which gives the opportunity to find non-resonant zones of the drive by the rotational and toothed frequencies of forced vibrations with the help of the frequency ranges of shafts. Conclusions: the developed software makes it possible at the design stage to simplify the dynamic system, find the lowest natural frequencies of torsional vibrations and take measures to exclude resonant phenomena.

On the effect of millimeter waves on DNA and RNA of viruses

Based on the differences between RNA and DNA, formulas for the natural frequency of torsional vibrations of single and double RNAs are obtained. It is shown that, despite the fact that millimeter waves are delayed by the skin of the human body, there are conditions under which they can freely penetrate through the human body. It is shown that centimeter waves, whose frequencies are multiples of the natural frequencies of torsional vibrations of the spirals of short DNA or RNA viruses, can cause subharmonic resonance in the spirals of RNA and DNA, which leads to the destruction of these molecules. Centimeter waves of non-thermal power flux density freely pass through the human body, which makes it possible to use them in vivo. A table has been compiled with the physical characteristics of DNA and RNA of the most dangerous viruses, indicating the frequencies of the external electromagnetic field that cause resonance in the DNA and RNA helices, which leads to the denaturation of molecules. In a series of experiments, it was shown that irradiation with microwaves with a resonant frequency of 180,402 GHz on samples with COVID-19 for 20 seconds. It has a disinfecting effect.

Master-slave synchronous control method for attenuating dual mode electromechanical transmission system torsional vibration

The high-power electromechanical transmission (EMT) system is a typical dual-mode hybrid power transmission system. The torque fluctuation of internal combustion engine causes serious shock and vibration problems of EMT. Suppressing torsional vibration based on high dynamic motor torque regulation is an important way to improve the working life and stability of EMT system. First, a lbased on the lumped parameter linear dynamic model,the torsional vibration characteristics are analyzed. Second, a fluctuating speed estimation method is proposed based on the uniformly accelerated motion model and linear regression, and a digital high pass filter is designed. Then, a master-slave coupling active torsional vibration control strategy is proposed, and a PD control algorithm based on speed feedback is designed. The variation rules of control parameters is analyzed. Finally, the control effect is verified by experiments. The results show that the lever coefficient K ab and differential coefficient K d of master-slave control can change the natural frequency of torsional vibration of the system, thus significantly changing the vibration response of the system. Selecting appropriate control parameters can achieve peak clipping of EMT torsional resonance.

The Analysis of a Generator Shaft Crack Cause by Torsional Vibration due to SSR

.This paper introduces the serious crack accident of the rotor of a 600 MW turbo-generator unit in Vietnam, which leads to the rotor scrapped. After excluding the material and design reasons, it is considered that the electrical torque is the possibility. Through the operation parameters and theoretical calculation of the unit, the fault reason is positioned as Sub-synchronous resonance. The most important criterion is that the vibration of Unit 1 increases simultaneously with that of Unit 2, which is physically isolated from Unit 1. Further theoretical calculation shows that the natural frequencies of torsional vibration are 13.74 Hz, 26.23 Hz and 30.30 Hz, which are complementary to the grid frequency at that time cause of the change of grid structure.

Research on coupled vibrations of driveshaft–rear axle system based on nonlinear hybrid model

The transmission shaft–rear axle system is consisted of universal joint, hypoid gear pair, tapered roller bearing, and half shaft. In this article, as a combination of system dynamics and structure dynamics, a hybrid dynamic model of the bending–torsional–shaft vibration of the driveshaft main reducer was established to study its noise vibration harshness performance. Through dynamic frequency sweep analysis, it is found that the natural frequency of torsional vibration of the system is 53.96 Hz. Getting the natural frequency of the torsional vibration of the systems being 57 Hz by the bench tests and Adams simulations. The correctness of the nonlinear hybrid model of the driveshaft–rear axle system is proved. This research will be beneficial to the design, monitoring, and fault detection of the automobile transmission system.

Diagnostic Damage Control of Shaft Trains in Turbine Units According to Torsional Vibration Parameters

An analysis of existing methods for determining the natural frequencies of torsional vibrations of the shaft trains in power turbine units is carried out in order to assess the potential for using changes in natural frequencies to diagnose shaft damage. A computational modeling of torsional vibrations of a shaft train having a circumferential crack allowed informative natural frequencies to be determined for the purposes of detecting damages and the locations of natural frequency measurements to be established to a satisfactory degree of accuracy. An assessment of changes in natural frequencies from depth and characteristic locations of a circumferential crack is carried out. An alternative method for detecting violations of the shaft train integrity, based on monitoring changes in the angles of static twisting, is also considered.

Диагностический контроль повреждений валопроводов турбоагрегатов по параметрам крутильных колебаний

The methods of solving the natural frequencies of torsional vibrations of power turbines shaft is done. Determination of shaft damage by changing the natural frequencies of torsional vibrations. A model of a shaft line with a circumferential crack has been created. The calculated torsional vibrations of the shaft line model with a circumferential crack are determined. A technique has been created for determining damage to the shaft line and the necessary measurement accuracy. Calculation of changes in the natural frequencies of torsional vibrations from the location of a circumferential crack. Shafting diagnostics for monitoring changes in the angles of static twisting

Оценка собственных частот крутильных колебаний композиционного нелинейно вязкоупругого вала

Оценка собственных частот крутильных колебаний композиционного нелинейно вязкоупругого вала

Results from Investigations of Torsional Vibration in Turbine Set Shaft Systems

The article generalizes the results obtained from investigations of torsional vibration in the shaft system of the T-175/210-12.8 turbine set installed at the Omsk CHPP-5 combined heat and power plant. Three different experimental methods were used to determine the lowest natural frequencies of torsional vibration excited in the shaft system when the barring gear is switched into operation, when the generator is synchronized with the grid, and in response to unsteady disturbances caused by the grid and by the turbine control and steam admission system. It is pointed out that the experimental values of the lowest natural frequencies (to the fourth one inclusively) determined using three different methods were found to be almost completely identical with one another, even though the shaft system was stopped in the experiments carried out according to one method and the shaft system rotated at the nominal speed in those carried out according to two other methods. The need to further develop the experimental methods for determining the highest natural frequencies is substantiated. The values of decrements for the first, third, and fourth natural torsional vibration modes are obtained. A conclusion is drawn from a comparison between the calculated and experimental data on the shaft system’s static twisting about the need to improve the mathematical models for calculating torsional vibration. The measurement procedure is described, and the specific features pertinent to the way in which torsional vibration manifests itself as a function of time and turbine set operating mode under the conditions of its long-term operation are considered. The fundamental measurement errors are analyzed, and their influence on the validity of measured parameters is evaluated. With an insignificant level of free and forced torsional vibrations set up under the normal conditions of turbine set and grid operation, it becomes possible to exclude this phenomenon from the list of main factors influencing the crack formation processes in low-pressure rotors. The importance of experimentally confirming the fact that the shaft system has been detuned from resonances at the 50 and 100 Hz excitation frequencies is pointed out.

Investigation of the torsional stiffness of flexible disc coupling

Calculation of flexible coupling torsional stiffness is required when analyzing the torsional vibrations of the reciprocating machinery train. While having the lowest torsional stiffness of all the elements of the train, flexible coupling has a significant influence on the natural frequencies of torsional vibration. However, considering structural complexity of coupling, precise definition of its torsional stiffness is quite a difficult task. The paper presents a method for calculating the torsional stiffness of flexible disc coupling based on the study of its finite element model response under the action of torque. The analysis of the basic parameters that quantitatively and qualitatively affect the coupling torsional stiffness has been also provided. The results of the calculation as well as model adequacy, sufficient for practical application, have been confirmed at the experimental measurement of flexible disc coupling torsional stiffness. The obtained elastic characteristics (dependences of applied torque and torsional stiffness versus twist angle) are nonlinear in the initial stage of loading. This feature should be taken into account when creating reliable mathematical models of torsional vibrations of reciprocating machinery trains containing flexible disc couplings.

Study on the Method of Online Adaptive Adjustment Method for Torsional Vibration Model of Turbine Shafting

The accuracy of safety analysis can be guaranteed when the torsional vibration model is adjusted online according to the inherent characteristics of the torsional vibration of the shafting. Torsional stiffness of model is set as the object for adjustment. The sensitivity of the natural frequency of torsional vibration model to structure parameters is analyzed and the sensitivity of the natural frequency of torsional vibration model to torsional stiffness is calculated. According to the difference between the natural frequency of torsional vibration which is get from actual shafting and the natural frequency of torsional vibration which is calculated by torsional vibration model, the adaptive adjustment of the torsional stiffness of mode is solved by using the method of Taylor expansion which ignore two times or more correction. The logic structure of the adaptive process of torsional vibration model is designed and the online adaptive function of torsional vibration model is implemented in the torsional vibration safety and analysis system. The torsional vibration modelof 1000WM turbogenerator is used as an example and the accuracy of the method is verified.

Sensitivity Analysis of 1000MW USC Units Shafting Torsional Vibration Based on ANSYS

To calculate a shaftings natural frequency of torsional vibration is one of the most important tasks in turbo-generators design, manufacture and frequency adjusting process. The sensitivity analysis of shafting structural parameters impact on the torsional vibration characteristics has important significance in reducing the amplitude of torsional vibration and ensuring the turbo-generators safe operation. In this paper, a 1000MW USC unit was taken as a research object to analyze the shaftings sensitivity to moment of inertia.

On the natural vibrations of the turbocompressor shaft with an artificial defect

The solution of the inverse problem of determining the origin coordinate and size of the turbocompressor shaft cross notch on three natural frequencies of torsional vibrations is presented.

English

The study of torsional vibration of rotor system is very important especially in application of high speed rotor. In the present work is extending the analysis of simple rotor to torsional vibration. The analysis of torsional vibration of the three rotor system of Agricultural pump with the conversional Newton’s second of motion or energy method. The analysis is extended to the system having different disc/ rotor dimension and different material. Where system natural frequencies of torsional vibration may be close to, or within, the source frequency range during normal operation, torsional vibrations constitute a potential design problem area. In such case designers should ensure the accurate prediction of design a rotor system based on torsional vibrations.

Damage detection of a flywheel shaft

Using three natural frequencies of torsional vibrations, it is possible to define the location and size of a transverse notch on the flywheel shaft.

Torsional vibrations and dispersion of torsional waves in orthotropic composite rods

The Barr’s refined theory of torsional vibrations of isotropic rods of noncircular cross section is generalized for an orthotropic material. An analysis of natural frequencies of torsional vibration of free-free orthotropic prismatic rods of rectangular cross section is carried out with the help of an exact solution of the frequency equation. For orthotropic CFRP and GFRP rods, the improved theory, which takes into account the normal stresses and inertia forces in the axial direction, in some cases, predicts a noticeable raise in the natural frequencies compared with those following from the Saint-Venant classical theory. A good agreement is obtained between the experimental and calculated values of natural frequencies of torsional vibrations of rectangular quartz and fiber glass rods. The dispersion of torsional waves in an orthotropic quasi-homogeneous rod is considered.

Characteristics of torsional vibrations of a shaft with unbalance

The aim of this paper is to study the characteristics of torsional vibration of a rotor with unbalance by numerical simulation. It can be concluded that synchronous torsional vibration accompanying with small higher harmonic components are excited, except when the speed of rotation is near, or equal to, half the natural frequency of torsional vibration, the bisynchronous component is much more remarkable than other harmonic components including the degraded synchronous one, and torsional vibration of the shaft can result in lateral vibration with bisynchronous frequency. Especially, when the rotating frequency is near the natural torsional frequency, where torsional vibration is strongest, the bisynchronous vibration becomes rather strong.